the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 24 Oct 2023
The characteristics of tides and their effects on the general circulation of the Mediterranean Sea
Emanuela Clementi
Anna Chiara Goglio
Nadia Pinardi
Abstract.
The effects of tides on the Mediterranean Sea’s general circulation, with a particular focus on the horizontal and vertical currents, are investigated using twin simulations with and without tides. Amplitudes of tides in the region are typically low, but an analysis of the kinetic energy demonstrates that tides have effects across many spatial and temporal scales in the basin, including nonlinear effects at short periods (less than one day) with high kinetic energy peaks at near-inertial, basin modes and tidal frequencies. Internal tidal waves are also revealed below 100 m. Tides are found to amplify several basin modes of the Mediterranean Sea, broaden several tidal frequency energy spectra bands, as well as interact energetically with near-inertial waves. Tides are found to increase the mixed layer depth in the Mediterranean Sea, particularly in the deep and intermediate water formation areas of the Western and Eastern basins. It is confirmed that the net mass transport through the Gibraltar Strait is unchanged by tides, but both inflow and outflow increase.
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Bethany McDonagh et al.
Status: open (until 19 Dec 2023)
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RC1: 'Comment on egusphere-2023-2251', Anonymous Referee #1, 26 Nov 2023
reply
The manuscript "The characteristics of tides and their effects on the general circulation of the Mediterranean Sea" by McDonagh et al. presents a study investigating the effect of tides on the Mediterranean Sea circulation. To my knowledge, this subject has not yet been extensively investigated. Apart from Sannino et al. 2014, which provided a first analysis of the tidal influence on the large-scale Mediterranean circulation, previous studies have only focused on specific areas such as the Alboran Sea (Sanchez-Garrido et al., 2013) or the Sicily Strait (Oddo et al., 2023; Gasparini et al., 2004). As such, the present manuscript proposes a valuable contribution to reinforce and deepen the current knowledge on the tidal influence on the Mediterranean Sea.
In this study, the authors diagnose the effect of tides from a pair of 5-year-long tidal and non-tidal experiments based on very similar numerical configurations. The first and second sections of the manuscript investigate the influence of tides on the Mediterranean Sea dynamics through the prism of sea level and kinetic energy spectra. These analyses focus on three specific locations: the Strait of Gibraltar, the Tyrrhenian Sea, and the Cretan Sea. They reveal that tides impact high-frequency (> 1 day⁻¹) dynamics through the propagation of the main tidal harmonics at work within the Mediterranean Basin and their interaction with various basin-scale modes. Then, the authors relate the tidally enhanced dynamics and mixing to the deepening of the mixed layer depth in the tidal simulation. The two final sections discuss the impact of tides on the thermohaline properties of the Mediterranean Sea and the transports through the Strait of Gibraltar.
Overall, the manuscript has the potential to provide valuable results on tidal contribution to Mediterranean dynamics. However, further work must be done before it can be accepted. More specifically, I think that although the two first sections of the manuscript provide valuable results, they focus on too specific areas to provide an overall picture of the tidal influence on the high-frequency Mediterranean dynamics. In addition, to assess the influence of tides on the "general circulation of the Mediterranean Sea", as stated in the the title of the study, the manuscript should investigate the influence of tides on the long-term, large-scale circulation. Regarding the impact of tidal dynamics, section 5 should more clearly distinguish the influence of local tidal mixing at the strait of Gibraltar, which impacts the Mediterranean mixed layer depth indirectly by changing the density of Atlantic water masses, and the less intense mixing induced by tidal currents throughout the Mediterranean Sea. The former is not directly related to the interaction of tides with the Mediterranean circulation, and it has already been investigated with similar model configurations (Sannino et al., 2014; Naranjo et al., 2014). Thus, I suggest not including it in this manuscript. On the other hand, the mixing induced by tidal dynamics is relevant to this study. Finally, sections 6 and 7 are, in my opinion, outside of the scope of this paper. Although interesting, the corpus of these sections has no apparent link with Mediterranean circulation and mainly emphasizes the conclusions of previous studies without additional results.
For these reasons, I am arguing for a major revision of the manuscript. Specifically, I would suggest:
- In sections 3 and 4: Add 2D maps of the tidal influence over the specific frequency bands mentioned in the text to give further confidence in the spatial extension of the results discussed.
- In section 5: If you intend to show that the tide-enhanced high-frequency dynamics are responsible for the deepening of the Mediterranean mixed layer depth, you should:
(1) Mostly focus on the overall increase of the mixed layer depth rather than its local increase over deep convection areas, where the intensity of tidal mixing is unlikely strong enough to drive the deepening.
(2) Look at the seasonal cycle of the mixed layer depth and stratification, as it would be easier to separate the effect of local vertical mixing from that of the tide-induced densification of Atlantic water masses at the Strait of Gibraltar. - Add some results on the influence of tides on the Mediterranean large-scale circulation, or reformulate the title of the article only to consider the high-frequency dynamics.
- Put sections 6 and 7 in the supplementary materials or a "model validation" section, demonstrating the consistency of the model with previous studies.
I do encourage authors to make the necessary effort to improve this manuscript. You can find general and detailed remarks, as well as references, in the attached PDF.
Bethany McDonagh et al.
Bethany McDonagh et al.
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